I had a 10 inch"medium stall" from A&A behind a 408 in a 3450 lb car with 3.55 gears. It would flash to 4000 when i went WOT but would settle in at about 10 percent slip at cruise of 65 to 70 mph. A stock converter would probably slip 7 percent under the same conditions. At least that is what i saw in my dart. I had a lockup trans in it with the same gears and would see over 200 rpm slip at cruise speeds when not locked up.